The low absorption loss, high sensitivity, and flexible light detection abilities of integrated optical waveguide analyte sensors make them suitable for many practical biological and chemical environments. Such analyte sensors include attenuation total reflection (ATR) [See, e.g., J. E. Midwinter in “On the use of optical waveguide techniques for internal reflection spectroscopy,” IEEE J. Quantum Electron. 7, pp. 339-344 (1971)], Raman scattering waveguide (RSW) [See, e.g., Y. Levy et al. in “Raman scattering of thin films as a waveguide,” Opt Commun. 11, pp.66-69 (1974)], and florescence spectrometry [See, e.g., W. M. Reichert et al. in “Excitation of fluorescent emission from solutions at the surface of polymer thin-film waveguides: an integrated optics technique for the sensing of fluorescence at the polymer/solution interface,” Appl. Spectrosc. 41, pp. 636-640 (1987); U.S. Patent Application Publication No. US2006/0019244, Jan. 26, 2006 for “Planar Optical Waveguide Based Sandwich Assay Sensors And Processes for The Detection Of Biological Targets Including Protein Markers, Pathogens And Cellular Debris”; and U.S. Patent Application Publication No. US 2003/0132406, Jul. 17, 2003 for “Sensor Element For Optically Detecting Chemical Or Biochemical Analytes.”].
Analytes are substances or chemical constituents undergoing analysis. Florescence-based waveguide analyte sensors rely on the use of excitation of a tag or label, such as a fluorescent dye, by excitation light guided in the waveguide with subsequent detection of florescence at a wavelength different from the wavelength of the excitation. Analytes may be dissolved in appropriate solvents therefore or may be suspended in fluids.
Present non-florescence-based optical waveguide analyte sensors rely on the optical properties of an analyte, such as refractive index or absorption, to alter the phase or amplitude of the light propagating in the waveguide. Included are an optical waveguide core; an optical waveguide lower cladding having a refractive index lower than that for the core; a photodetector; and optionally a substrate for additional mechanical support. Light is directed through the core, and evanescent portions of the optical field penetrate into regions near the core including the analyte and the lower cladding. The photodetector is positioned at the end of the waveguide to intercept the intensity of light traveling in the core which is responsive to changes in the evanescent field resulting from the interaction between the evanescent field and the analyte in contact with a portion of the exterior of the waveguide [See, e.g., U.S. Pat. No. 5,144,690 for “Optical Fiber Sensor With Localized Sensing Regions” which issued to Lawrence H. Domash on Sep. 1, 1992; and U.S. Pat. No. 5,991, 479 for “Distributed Fiber Optic Sensors And Systems” which issued to Macros Y. Kleinerman on Nov. 23, 1999.].
Interferometric waveguide structures including Mach-Zehnder interferometers consisting of multiple waveguides that are coupled at two or more points along their lengths may be employed; however, a photodetector positioned at the terminus of one or more of the waveguides is used to detect the light propagated in the core. Light may be introduced into the waveguide using either end-fire, prism, or grating coupling techniques that are well known to those skilled in the art.
An alternative is to use a prism to permit the light to exit the waveguide away from the sensor region and direct the light coupled out through the prism to a detector. Such configurations permit only one analyte to be sensed with each waveguide.
Conventional ATR and RSW waveguide analyte sensors are often limited in the number of analytes that can be simultaneously detected by one sensor, and require complex sample preparation; that is, the large size and non-local detection characteristic of these sensors diminishes their applicability to complex and multiple analyte environments. Additionally, sensors using florescence spectrometry require that the target samples be prepared with chemically specific dyes or labels which increases the complexity and overall cost for analyses.
Accordingly, it is an object of the present invention to provide an apparatus and method for detecting analytes.
It is another object of the invention to provide an apparatus and method for simultaneously or individually detecting multiple analytes.
It is yet another object of the invention to provide and apparatus and method for detecting multiple analytes without requiring markers, such as fluorescent tags, attached to the analytes.
Additional objects, advantages and novel features of the invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.